Shoulda is intended for unit testing, and becomes available in Ruby projects on attaching the shoulda gem. So doing, the Shoulda tests are added on to the Test::Unit framework.

RSpec. This testing tool supports BDD. RSpec becomes available in Ruby projects on attaching the rspec gem. For the Rails applications, rspec-rails gem is also required.

MiniTest becomes available on attaching the minitest-reporters gem. The minitests are added to the Test::Unit framework.

Cucumber. This testing tool supports BDD, and enables using features and scenarios written in a human-readable language, either English or any other language specified in the # language: comment. Cucumber becomes available in project upon installing and activating the cucumber gem.